The purpose of this study is to describe a Phase II study, in patients with advanced hormone refractory prostate cancer and evaluable patients with metastatic or locally advanced renal cell carcinoma, of the safety, toxicities, and clinical efficacy of MDX-H210, a bispecific antibody that recognizes HER2/neu and the high affinity Fc(gamma)RI receptor, in combination with GM-CSF. Patients will receive an intravenous infusion of BsAb at 15.0 mg/m^2 on study days 4,11, and 18. Bispecific antibody may be administered on either an in-patient or out-patient basis at the discretion of the principal investigatior. Patients will be admitted to the hospital to manage significant toxicity if it occurs. Physical examination and laboratory testing will be used to monitor patient safety and toxicity. BsAb binding to tumor target tissue, and immunologic assays will be performed. In selected patients, monocytes/neutropils will be labeled with Tc-99 to test their ability to traffic to tumor tissue after GM-CSF therapy. In patients with measurable disease, preliminary assessment will be made of anti-tumor responses. In patients with evaluable disease (e.g. bone metastasis), evaluation of the disease will be made by radiologic and serologic methods. All the patients will be assessed for symptomatic benefits using a quality of life monitoring system.